-A+B+C=-(x2 -2x+3xy2-x2y+x2y2)+(-2x2+3y2-5x+y+3)+(3x2-2xy+7y2-3x-5y-6)
-A+B+C=-x2+2x-3xy2+x2y-x2y2-2x2+3y2-5x+y+3+3x2-2xy+7y2-3x-5y-6
-A+B+C=-x2-2x2+3x2+3y2+7y2+2x-5x-3x+y+-5y+3-6+x2y-x2y2-2xy-3xy2
-A+B+C=(x2-2x2+3x2)+(3y2+7y2)+(2x-5x-3x)+(y-5y)+(3-6)-x2y+x2y2+2xy+3xy2
-A+B+C=(2x2)+(10y2)+(-6x)+(-4y)+(-3)-x2y+x2y2+2xy+3xy2
-A+B+C=2x2+10y2-6x-4y-3-x2y+x2y2+2xy+3xy2
Bậc của đa thức trên là 4.